As the number of circuits per unit area has increased in integrated circuits, particulates have become more of an issue associated with semiconductor wafers during their conversion into the integrated circuits. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level. Particulate control is necessary during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers. Particle generation during insertion and removal of wafers into carriers and from movement of wafers in carriers during transport needs to be minimized or avoided. Wafer containers are washed to remove particulates that have accumulated during use. Such containers need to be constructed to minimize any contamination issues associated with said washing. Such issues include areas that do not immediately dry after washing and contaminants introduced by washing fluids coming into contact with metallic components. Driven by economies of scale, the size of wafers utilized in semiconductor fabrication facilities (“fabs”) has continually increased. Currently there are a number of fabs that process 300 mm wafers and fabs for 450 mm wafers are being developed.
The 300 mm and 450 mm diameter wafers are carried and handled with front opening wafer containers. Contained within is a spaced stack of horizontally oriented wafers supported by shelves and wafer restraints. The bottom of the container has kinematic coupling to precisely seat on a machine interface with cooperating kinematic coupling projections and a robotic flange for grasping and conveying of the containers. The front opening wafer containers include a door that is disposed on a forward side of the wafer carrier. The door is sealingly coupled to and seated within in a frame. The door and frame present added weight at the front extremity of the wafer container, causing a significant moment arm that causes the wafer container to pitch forward. That is, the center of gravity of the wafer container is substantially ahead of the geometric center of wafer container, even when the wafer container is fully loaded. Door opening and closing, and wafer removal and insertion are all accomplished robotically. Precise, stable, and secure seating of the front opening wafer container on the machine interface is imperative. Issues associated with precise seating and stability that may be present in 300 mm wafer containers are exacerbated with the 450 mm containers due to the greater expanses of plastic, thicker walls, and significantly greater weight.
The bottom kinematic coupling is typically provided on a kinematic coupling plate that has three aligned slots that seat on a kinematic coupling comprising three rounded projections arranged in a triangle for precise location of the kinematic coupling plate. A central axis extends through the center of a square robotic flange positioned on the top of the container. The central axis also passes through a centrally located position between the three aligned slots and the three projections engaged with the slots when the carriers are seated. In some instances, the central axis extends vertically through the stack of spaced wafers in both 300 mm and 450 mm front opening containers.
It is advantageous for stability and optimal seating to have the center of gravity of the wafer container positioned at or in close proximity to the central axis that corresponds to a center of the three projections of the kinematic coupling and the center of the square robotic flange on the top of the wafer containers. Accordingly, certain aspects of the 300 mm and 450 mm containers have been standardized by industry standards promulgated by Semiconductor Equipment and Materials International (“SEMI”), know as SEMI standards. SEMI standards E158 and E159 specify that the center of gravity be within a certain distance of the central axis of the robotic flange in a direction that is forward of the central axis, “forward” being in a direction towards the door of the wafer container. For example, the center of gravity is specified to be within 29 mm of the central axis in the forward direction for 450 mm Front Opening Unified Pods (“FOUPs”), and within 39 mm of the central axis in the forward direction for 450 mm Multiple Application Carriers (“MACs”).
A system that can be implemented with both new and existing wafer containers to adjust the position of the center of gravity of front opening wafer containers would be a welcomed addition to the wafer container art.